1. Field of the Invention:
This invention relates generally to an input level display circuit for receivers, and more particularly to a receiver that has an indicator circuit connected to both first and second input circuits to be energized thereby.
2. Description of the Prior Art:
In an FM-AM tuner, in order to indicate its input level, an FM intermediate frequency signal or AM intermediate frequency signal is rectified, then a direct current signal corresponding to its input level is obtained, and the direct current signal is supplied to a tuner input meter, as in the prior art.
In such a case, a problem arises if an input level indicating device, namely, an input meter, is desired in a receiver suitable for the reception of AM signals as well as FM signals. The indicating device has to be controlled on FM signal reception in a manner different from AM signal reception. It is objectionable to provide an additional switch section on the AM/FM switch intended for switching over the receiver from AM signal reception to FM signal reception for this purpose, on the one hand, because this results in a switch which is more costly and takes up more space and, on the other hand, because it is usually necessary for this purpose to provide long conducting wires in the receivers leading to the switch.
Further, AM/FM receivers at present have stages such as RF, IF, descriminator, or multiplex stages formed as integrated circuits. Due to the employment of an integrated circuit, the receiver can be easily assembled and becomes long in life since the respective parts are solid state. However, as described above, it is not appropriate for a receiver using an integrated circuit to have a switch for indicating signal strength of AM or FM signals on an input level indicating device. An ordinary switch has a mechanical contact and is apt to be damaged and short in life as compared with an electronic switch. This is counter to utilizing the advantages of a receiver made of an integrated circuit.